1. Field of the Invention
The present invention generally relates to an external control type fan-coupling device of a system for controlling the rotation of a fan for cooling an engine in an automobile, etc. by following-up a temperature change of the external circumference or a rotation change.
2. Description of Related Art
The following fan-coupling device is conventionally known as the fan-coupling device of this kind. Namely, in this fan-coupling device, a drive disk is fixedly attached to the tip of a rotating shaft body (drive shaft). A seal device housing is constructed by a case of a nonmagnetic material supported on the rotating shaft body through a bearing, and a cover attached to this case. The interior of the seal device housing is partitioned into an oil reservoir chamber and a torque transmitting chamber for internally mounting the drive disk by a partition plate having a supply adjusting hole of oil. A valve member having a magnetic property opening and closing an oil circulating flow passage formed between the above torque transmitting chamber and the oil reservoir chamber is arranged within the oil reservoir chamber. The opening and closing of the above oil circulating flow passage are mechanically controlled by operating the valve member by an actuator. The transmission of rotation torque from the drive side to the driven side is controlled by increasing and decreasing an effective contact area of the oil in a torque transmitting clearance portion formed by the drive side and the driven side.
As the external control type fan-coupling device of this kind, there is an external control type fan-coupling device of a system for operating the actuator within the coupling device by magnetizing an electromagnetic coil fixed to the engine or the vehicle body side, and controlling the fan rotation from the exterior (see U.S. Pat. No. 6,443,283). Its structure is set to a system constituting a magnetic loop for transmitting a magnetic flux using the magnetization of the electromagnetic coil to the valve member through a magnetic path of a magnetic material (a shaft and a valve member) of high magnetic permeability, and again returning the magnetic flux to the electromagnetic coil. A voltage is applied to the electromagnetic coil by an input signal from ECU. The flow rate of the torque transmitting oil is controlled by opening and closing the valve member within the coupling device by this electromagnetic force.
However, there are defects described below in the case of the above conventional external control type fan-coupling device.
Namely, in the case of the system for performing an operation by transmitting the magnetic flux for magnetizing the electromagnetic coil fixed to the exterior to the valve member within the coupling device, it is necessary to construct the magnetic loop for transmitting the magnetic flux using the magnetization of the electromagnetic coil to the valve member through the magnetic path of the magnetic material (a shaft and the valve member) of high magnetic permeability, and again returning the magnetic flux to the electromagnetic coil. Therefore, there are the following defects, etc. Namely, there is a restriction of a layout in the position relation of the electromagnetic coil and the valve member. The case and the valve structure become complicated. There is a fear that the oil is leaked by assembling magnetic material parts for constructing the magnetic loop into the coupling device. Magnetic leakage is much since a magnetic circuit is long. The general purpose property of the system with respect to the fan-coupling device different in size is poor.